From the 1917 Code of Canon Law:
566. Of special note for Passion-tide: before the First Vespers of Passion Sunday, i.e., before noon on Saturday, all the crosses in the church and the statues on the altar shall be veiled. (S.R.C. 1275 ad 2). The statues of the saints are uncovered at the Gloria in Excelsis on Holy Saturday.
567. This veiling, or covering, shall be of violet color, and not transparent; it shall be embroidered with no figures, not even the cross. (Martinucci, II, 21.). The pictures, or images, of the fourteen Stations of the Way of the Cross may be left uncovered during Passion-tide. (S.R.C. 3638 ad 2.).
568. 1. During Passion-tide it is not permitted to uncover the statues should the feast of the Titular, or of the Dedication of the Church, or of St. Joseph occur. (S.R.C. 926 ad 2 and 3; 3396).
2. If out of devotion to St. Joseph the statue of the saint is exposed during the month of March outside the altar, may it not be left uncovered during Passion-tide? The Sacred Congregation of Rites, 3448 ad 11, answered: "Tolerari posse." "It may be left uncovered."